Radiance based diagnostics of body tissues involves radiating a body tissue and obtaining data relating to the transmittance or reflection of the radiated light from the tissue, for analysis of tissue constituents. For example, electro-optical measurement of blood characteristics has been found to be useful in many areas of blood constituent diagnostics, such as glucose levels, oxygen saturation, hematocrit, bilirubin and others. Pulse oximetry is a method for measuring oxygen saturation in the blood, in which two or more wavelengths are radiated through an organ at a point where blood perfuses the organ. Reflective pulse oximetry employs at least one light source and a least one detector which are placed at the same side of an organ. The light source is for radiating the organ and the detector is for receiving the light reflected from the organ. The reflected light is analyzed for measuring the percent of saturated oxygen in the blood.
These methods of body tissue diagnostics usually employ sensors, which are placed on body tissues, and which comprise at least one radiance source for radiating the tissue and at least one radiance detector, for detecting the rays transmitted through or reflected from the tissue. The accuracy of the results obtained in these methods depends, to a great extent, on ensuring that the detector, or detectors, is exposed only to rays which have passed through the examined tissue and not to other rays, such as rays coming directly form the radiance source.
When a sensor is placed on body tissues, especially on stretched tissues (such as over a bone), or due to irregular tissue surface (such as in wrinkles), there might be a small space between the face of the sensor and the tissue, through which some of the rays can pass directly from the radiance source to the detector, thereby adversely affecting the measurement.
Reference is now made to FIG. 1 which is a schematic side view illustration of a prior art sensor. The sensor, generally referenced 10, contains a light source 12 and a light detector 14. The sensor is placed onto examined tissue 16 and, when operated, light is radiated from light source 12 onto tissue 16. Depending on how the light source 12 is directed, most of the light will pass through the tissue 16 and be partly reflected from the tissue. The reflected light 14′ will be received by detector 14 to be analyzed. However, a small fraction of the light 18′ radiated from the light source 12 will not pass through the tissue 16 but pass directly to the detector 14, through the small space 18 between the sensor 10 and the tissue 16. Since the detector can not differentiate between the two lights, 14′ and 18′, the analysis results will be inaccurate.